1. Field of the Invention
This invention relates to improvements in a float valve device which is adapted to make gas venting in a container for a liquid and to stop the gas venting when the liquid level reaches to a predetermined level.
2. Description of the Prior Art
Hitherto float valve devices have been known to be used with a container for a liquid in order to make gas venting of the container for a liquid and to stop the gas venting when the liquid level reaches to a predetermined level. A typical one of them is disclosed in U.S. Pat. No. 5,028,244 and arranged as follows: A float valve device is installed to the upper wall section of a fuel tank. During supply of fuel into the fuel tank, air and fuel gas within the fuel tank is vented out of the fuel tank and introduced into a carbon canister. When the fuel level in the fuel tank has reached a predetermined level, a float ascends to close a valve opening thereby stopping gas venting, thereby maintaining the fuel level to the predetermined level while preventing fuel leak to the side of the carbon canister even under shaking of the fuel level during vehicle turning or the like.
However, drawbacks have been encountered in the above-discussed conventional float valve device which is arranged such that the valve opening is closed upon contacting of the upper section of the ascending float with a peripheral portion of the valve opening. The upper section of the float and the peripheral portion of the valve opening are made of plastic and therefore makes a rigid contact therebetween (at a contacting or sealing surface), thereby making it impossible to accomplish a sufficient liquid tight seal. Additionally, the sealing surface between the upper section of the float and the peripheral portion of the valve opening is generally spherical thereby providing the following shorcomings: It is difficult to obtain a high fitting precision at the sealing surface, and also difficult to maintain a right spherical surface after the sealing surface has been subjected to various loads during operation of the float valve device. Furthermore, the spherical sealing surface will wear and deform under repeated operations of the float valve device. Moreover, if there is a misalignment between the axes of the opposite faces constituting the sealing surface, no sufficient sealing at the sealing surface can be obtained.